elasticsearch

Open Source, Distributed, RESTful Search Engine
 ElasticSearch is a distributed RESTful search engine built for the cloud.
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 Features include:
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 * Distributed and Highly Available Search Engine.
   - Each index is fully sharded with a configurable number of shards.
   - Each shard can have one or more replicas.
   - Read / Search operations performed on either one of the replica shard.
 * Multi Tenant with Multi Types.
   - Support for more than one index.
   - Support for more than one type per index.
   - Index level configuration (number of shards, index storage, ...).
 * Various set of APIs
   - HTTP RESTful API
   - Native Java API.
   - All APIs perform automatic node operation rerouting.
 * Document oriented
   - No need for upfront schema definition.
   - Schema can be defined per type for customization of the indexing process.
 * Reliable, Asynchronous Write Behind for long term persistency.
 * (Near) Real Time Search.
 * Built on top of Lucene
   - Each shard is a fully functional Lucene index
   - All the power of Lucene easily exposed through simple configuration / plugins.
 * Per operation consistency
   - Single document level operations are atomic, consistent, isolated and durable.
 * Open Source under Apache 2 License.